Extinction's Ripple Effect

Like doctors battling a deadly disease, conservationists go about their work knowing that many species will die out despite their best efforts. A new analysis in tomorrow's Proceedings of the National Academy of Sciences now adds to the gloom: It suggests that the loss of key primate species could drag down dozens of other species as well.

Ecologists know that losing a species that plays an important role in an ecosystem--such as birds that disperse seeds--can harm populations that rely on that species. Primatologist Patricia Wright of the State University of New York, Stony Brook, and her husband, evolutionary biologist Jukka Jernvall of Stony Brook and the University of Helsinki in Finland, sought to measure any ecosystem-wide ripples from losing particular species of primates, well-studied mammals that play key roles in many ecosystems.

The duo assumed two potential waves of extinction, the first wiping out all endangered primate species, the second vanquishing ones now listed as threatened. Next they examined 17 variables, including diet, habitat, tooth type, and body size, and used them to characterize each species' ecological role--as a predator or as a seed disperser, for instance. Finally, they forecasted how the range of ecological functions carried out by primates in a particular region might change as species die out.

The results varied dramatically by region. In South America, the researchers found, primate species fill a variety of ecological niches that can be filled by other species that also exploit those niches--so the impact of losing the vulnerable primates would be low. But primate species winking out in Asia, Africa, and especially Madagascar could spell big trouble for ecosystems, as entire guilds of primates with similar specializations--such as dispersing seeds--would be lost in a single clump. "After that, no primate is doing that job in the forest," Jernvall says. Such losses might hasten the decline of trees that depend on seed dispersers, and so affect other organisms, says Wright.

"It's an interesting exercise, but it doesn't get us that far in practical terms," says Ian Tattersall, a primatologist at the American Museum of Natural History in New York City, who says knowing the ecological effects of extinctions doesn't help much in staving them off. Still, ecologist Stuart Pimm of the University of Tennessee, Knoxville, thinks the work helps "bridge the gap" between studies of extinction and ecosystem productivity.